The present invention relates to a driving mechanism for a focal plane shutter, and more particularly to a driving mechanism for a focal plane shutter provided with a shock absorption mechanism capable of effectively absorbing shock at the end of forward movement of each blade group constituting the focal plane shutter with a simple structure.
A focal plane shutter for a recent single lens reflex camera attains high-speed operation of shutter blades in order to stabilize the exposure accuracy in a short exposure time and increase the synchronization speed of the electronic flash.
For example, a shutter was moved across a vertical distance of 24 mm from an upper end to a lower end of an aperture of a frame of a 35 mm type camera in about 7 ms several years ago, whereas it has been adapted to be moved in about 3 ms recently.
On the other hand, it is well known that operation sound and oscillation at the end of forward movement of the shutter blades are increased as the blade speed is increased. A focal plane shutter having a high blade speed requires an effective shock absorption mechanism.
A conventional shock absorption mechanism which includes a brake lever disposed in a path through which a blade driving member passes and pressed between a friction plate and a leaf spring so that the brake lever is rotated by striking the blade driving member against the brake lever and the kinetic energy of the blade driving member and the shutter blades is converted into thermal energy by friction of the friction plate and the brake lever to absorb shock is generally known.
However, the above-mentioned friction type shock absorption mechanism has many problems as described below.
The coefficient of friction between the members is effected by variation in temperature and aging and accordingly the shock absorption performance tends to be varied.
Since the brake lever and the friction plate for the shock absorption are provided in addition to the shutter driving mechanism, the number of components are increased and the space factor is reduced.
The shock absorption mechanism must also be set at the time of the setting operation in addition to the shutter driving mechanism and accordingly the setting force is increased.
U.S. Pat. No. 4,975,722 discloses a mechanism for utilizing a single spring as a source of driving force and a source of braking force. However, in accordance with this patent, since a blade driving lever 18 and blade brake lever 15, the number of components is increased and the space factor is reduced.